New Flu Drug from Japan Doing Well in U.S. Clinical Trials

As the United States braces for what’s likely to be another deadly flu season, a drug that could kill the virus faster than current medications has inched closer to becoming available to U.S. consumers.

The results of a clinical trial of the drug, developed in Japan and requiring just a single dose, were published last week.

Baloxavir marboxil, which goes by the brand name Xofluza in Japan, was shown to alleviate flu symptoms in 54 hours and, most exciting for infectious disease experts, to likely have a significant effect on cutting down on the transmission of the virus.

The drug is currently up for “priority review” by the U.S. Food and Drug Administration (FDA).

A decision is expected from the FDA by December 24, although it isn’t clear how soon after that it could be on pharmacy shelves if it does get approval.

The 54 hours to eliminate symptoms isn’t different from that of Tamiflu, the most similar drug currently available. However, Tamiflu typically requires five days of twice-daily doses to eliminate symptoms, during which time the virus can still be spread to other people.

Baloxavir, on the other hand, requires just one dose. And it has an antiviral effect within one day of that dose that’s almost 100 times greater than Tamiflu, according to Dr. Frederick Hayden, who led the clinical trial at the University of Virginia School of Medicine.

“The thing that’s the most impressive to me in our study was the magnitude of the antiviral effect, much greater than placebo and significantly greater than (Tamiflu),” Hayden told Healthline. “That gives me some hope that this drug will be effective in reducing flu complications and perhaps in reducing transmission.”

Previous reports of baloxavir’s effectiveness against flu symptoms said the new drug kills the virus within 24 hours.

Hayden said that timeline was likely misreported, although he noted that it was able to dissipate fevers within 24 hours, and that in some people symptom alleviation occurred within 24 hours — though the median time was 54 hours.

Schaffner, who wasn’t involved in the trial or the development of the new drug, said it’s possible H3N2 is to blame for that delay.

“The initial stories that came out of phase one (trial) were that symptoms abated very, very rapidly,” he told Healthline. “But now it’s taking longer. That’s not surprising because it’s more realistic.”

Trials take place in the real world, Schaffner noted.

“You don’t infect the patients,” he explained. “You wait for them to get infected in nature. And the dominant strains from year to year are different.”

Greater prevalence of H3N2 now would make it tougher for a drug to combat, he said.

But Schaffner was still “very excited” about the possible implications of having a drug that could potentially more quickly stop the spread of flu from person to person.

“Use of this drug has the potential to limit transmissions very substantially,” he said.

Part of the reason for that is the single dose.

Even if baloxavir doesn’t cure people any faster than Tamiflu, one dose versus a five-day course of medication could be a big improvement.

“People might stop a five-day regimen when they start feeling better. That’s not a good thing,” Hayden said.

He said when reviewing the trial results he noted that some viruses developed resistance to baloxavir.

That resistance has never been a concern with Tamiflu, he said, because of the way the drug interferes with the multiplication of the virus in the body, so there’s never been concern over using too much Tamiflu.

Baloxavir interferes in a slightly different way and that could be a problem to keep an eye on, Schaffner said.

But, he noted, the baloxavir-resistant viruses were still resistant to Tamiflu in the trials.

“So we always will have Tamiflu in our holster,” Schaffner said.

That could mean the new drug will be part of a flu-fighting toolbox rather than a panacea.